In examinations using x-ray radiation, the patient or organs of the patient in an area to be examined exhibit very different absorption behavior with respect to the applied x-ray radiation. For example, in thorax images, the attenuation in the area in front of the lungs is very large on account of the organs arranged in the area in the front of the lungs. The attenuation is very small in the area of the lungs itself. In order both to obtain a meaningful image and also, for example, to protect the patient, the applied dose may be adjusted depending on the area such that no more x-ray radiation than is required is supplied. This provides that a larger dose is to be applied in areas with a large attenuation than in areas with a lower attenuation. In addition, there are applications in which only part of the examined area is to be imaged with a good diagnostic quality (e.g., with little noise). The surrounding parts are important for the orientation but not for the actual diagnosis. These surrounding areas may therefore be imaged with a lower dose in order to reduce the overall dose applied.
Filters are used to attenuate x-ray radiation. A filter of this type is known, for example, from DE 44 22 780 A1. The filter has a housing with a controllable electrode matrix, by which an electric field that acts on the fluid connected to the electrode matrix, in which fluid ions absorbing x-ray radiation are present, is generated. These are freely moveable and move around as a function of the applied field. By virtue of the corresponding electrical field, more or fewer ions may be accumulated correspondingly in the area of one or several electrodes in order to locally change the absorption behavior of the filter.